Broadly speaking, DC to AC power converter converts DC power received at an input to AC power for outputting to a load. Typically, DC to AC power converters comprise a plurality of power switching devices, a transformer, a rectifying circuit, an intermediate DC stage and an output current shaping circuit. A plurality of power switching devices in the input path to the transformer are switched to convert the DC input voltage to an AC current, which is magnetically coupled by the transformer to the output side of the transformer.
Typically, the ac current in the output path of the transformer is full-wave rectified, for example using a rectifying diode bridge, to produce an intermediate DC signal in an intermediate DC stage, such as a Buck stage. The intermediate DC signal is current-shaped by switching a plurality of power switching devices in order to shape the output current to conform to a desired ac output current waveform. In such a configuration, the number of power switches is large, typically 8 to 12 or more.
We have appreciated the problems associated with using a large number of power switches in such a DC to AC power converter. The large number of power switching devices and the circuits necessary to control such devices decrease the overall efficiency of the circuit as each power-switching device has associated losses intrinsic to the device. Therefore, the larger the number of switching devices, the larger the losses and the lower the efficiency.
We have appreciated the need to reduce the number of power switching devices used in a DC to AC power converter.